How do I clear sharp edges on my models / apply one smoothing group to the whole piece?
You only need to clear sharp edges if they have been marked sharp in the first place, If you are unsure, go to edit mode, select the whole object (all), right click, and select &quot;clear sharp&quot;. See below:

And yes - one smoothing group means select the whole thing (in object mode) and select &quot;shade smooth&quot; - this is to differentiate from some models which have different sections selected, and smoothing applied to only those sections.